Recently, there has been rapid growth in the use of various optoelectronic products. Optoelectronic products require an optical interface to communicate between the human and the optoelectronic product or require an optical device installed within the optoelectronic product such as an LCD display and a digital camera. Due to decreasing sizes of optoelectronic products, not only do the manufacturing processes of related circuits need to advance, but also the size of related optical parts needs to decrease accordingly. If a traditional optical device is forced to meet the requirement of current portable products, its advantages, such as weight and convenience, will be lost. Therefore, MEMS technology and precise machining are both utilized in optical devices in portable products, since there is no difference between the utilizations of light scale by micro-optics and by traditional optics. In particular, MEMS technology is capable of batch and mass production and thus suitable for manufacturing of current portable consumer products.
Currently the microlens is commonly used in the systems of optical fiber communication, display, biomedical diagnosis and optical storage equipment. Focus spot resolution provided by the microlens determines the performance of the systems. However, an adequate focus spot resolution provided by a general microlens cannot be obtained due to spherical aberration, and in micro optical systems the issue of spherical aberration cannot be resolved by the combination of plural spherical lenses. Therefore, it is necessary to develop the micro-aspherical lens to provide better optical quality.
The manufacturing of traditional large-scale lenses, including spherical lenses and aspherical lenses, can be achieved by precise machining under tight controls. When the size of the lens shrinks down to a scale of a micro-system ranging from centimeters to sub micron, a delicate control method is required and the manufacturing process is time-consuming if a traditional machining process is used to manufacture a micro-aspherical lens.
In 2003, D. W. de Lima Monteiro et al. (refer to “Single-mask microfabrication of aspherical optics using KOH (potassium hydroxide) anisotropic etching of Si”, OPTICS EXPRESS, Vol. 11, No. 18, 8 Sep. 2003) proposed a method to fabricate a micro-aspherical lens using a single-mask and anisotropic etching. The method needs to consider the issue of surface roughness and the rounded profile after KOH anisotropic etching approximates an aspherical lens. However, this method can be used for batch production of reflective and refractive aspherical surfaces. Once the lens is fabricated by this method, with a fixed shape, it cannot subsequently be modulated to change its optical characteristic.
In another prior art, Nikolas Chronis et al. (refer to “Tunable liquid-filled microlens array integrated with microfluidic network”, OPTICS EXPRESS, Vol.11, No. 19, 22 Sep. 2003) proposed a pneumatic microlens whose focal length is dynamically adjusted by pneumatically controlling the pressure with the microfluidic network. In this method, a microfluidic network is integrated on the bottom of the array to deliver and pressurize the liquid into the circular chambers that are pre-filled with any liquid whose index of refraction is equal or higher than that of PDMS (polydimethylsiloxane) in order for a positive plano-convex lens array to be formed. A pneumatic pump having a pressure regulator is used to inflate the PDMS membrane. However, the tunable micro-aspherical lens with a pneumatic pump is not compatible to general optoelectronic products and the tunable range is limited to one dimension, resulting in spherical aberration at the edge.
Philips (refer to http://www.research.philips.com/newscenter/archive/2004/fluidlenses.html) provides a variable-focus lens system using the interface of two immiscible fluids of different refractive indices and electrowetting effect. The modulation of a lens by electric field is proved to be feasible by commercialization of Philips′ variable-focus system; however, the tunable range thereof is limited to one dimension.
To meet rapid growth and miniaturization of consumer products, the development of new-generation micro optical devices with better optical quality has become a worldwide target. In particular, personal demand for portable optoelectronic products and improvement of the functionality thereof make the large-scaled aspherical lens with improved focus a main product of optical manufacturers. In these times of micro-scaled technology growth, the demand for the micro-aspherical lens is expected to be promising.